Future cellular equipment types such as handsets, notebook computers, and tablet computers will require simultaneous transmission of signals at two different frequencies, referred to as multi-carriers. These multi-carriers require a wide bandwidth for each carrier. Each of the multi-carriers typically require up to 20 MHz of bandwidth. Long term evolution (LTE-Advanced) as currently defined allows for the possibility of multi-carrier transmission in a single band or in different bands. As a result, LTE-Advanced customers will be afforded relatively large data rates.
FIG. 1 is a spectrum diagram that demonstrates a peak data rate increase via a bandwidth increase. In this case, five multi-carriers each having a 20 MHz bandwidth can yield up to 100 MHz of total bandwidth for a given user.
FIG. 2 is a spectrum diagram depicting intra band component carriers (CC) that are contiguous within a band A. For this case, the multi-carriers are aggregated in the spectrum allocated to band A. Therefore, a typical power management system having a modern fast power converter referred to herein as a switcher can be used to drive a single power amplifier (PA) for transmitting multi-carriers that are contiguous within the band A. However, bandwidth requirements for the typical power management system can be exceeded even while using intra band component carriers (CC) that are contiguous within a single band.
FIG. 3 is a spectrum diagram depicting intra band CC that are non-contiguous within the band A. In this case, the problem of increased bandwidth requirement for a power management system is made even worse since the spectrum is not used in a contiguous manner.
FIG. 4 is a spectrum diagram depicting inter band CC within the band A and within a band B. The bandwidth requirement for a power management system is even greater in this case since multi-carriers are spread among the band A and the band B.
FIG. 5 depicts a related art power management system 10 that drives a single power amplifier (PA) 12 for multi-carriers. The power management system 10 includes a full size switcher 14 that converts power from an energy source such as a battery (not shown) to power levels that are appropriate for the single PA 12.
An output filter 16 that is coupled to an output node 18 of the second switching power supply is continuously coupled between the full size switcher 14 and a power supply node 20 of the single PA 12. The output filter 16 is an LC type filter for reducing output ripple voltage that is a component of a dynamic voltage output from the full size switcher 14. The output filter 16 includes an inductor LLINEAR coupled between the output terminal 18 and the power supply node 20 of the single PA 12. A capacitor CLINEAR is coupled between the inductor LLINEAR and a fixed voltage node such as ground GND. Typically, the inductor LLINEAR has an inductance value of a few nH, while the CLINEAR capacitor has a capacitance value of a few nF. For example, the inductor LLINEAR has an inductance value that ranges from about 1 nH to 10 nH, and the first capacitor CLINEAR has a capacitance value that ranges from about 1 nF to 10 nF.
An operational amplifier (OPAMP) 22 drives the full size switcher in response to an analog control signal VRAMP coupled to a first OPAMP input 24. An output 26 of the OPAMP 22 is coupled to a control input 28 of the full size switcher 14. Alternating current AC components are passed from the output 26 of the OPAMP 22 through an output capacitor COUT that is coupled between the output 26 and the power supply node 20. A sample of a common collector voltage (VCC) pseudo envelope following (PEF) signal is coupled from the power supply node 20 to a second OPAMP input 30. An enable signal EN is usable to enable and disable the single PA 12.
FIG. 6 is a spectrum diagram that depicts a VCC bandwidth (BW) of the full size switcher 14 for dual carriers that provide modulation for the single PA 12. In particular, the modulation bandwidth of the full size switcher 14 is a function of an offset frequency Df between a carrier #1 and a carrier #2. Therefore, the higher the offset frequency Df between the carrier #1 and the carrier #2, the higher the modulation bandwidth must be. At some point, the offset frequency Df is large enough that related art approaches for modulating the VCC PEF via the full size switcher 14 are no longer practical. Moreover, even if the offset frequency Df is equal to zero between two adjacent carriers having a 20 MHz bandwidth each, a resulting 50 MHz VCC BW is too large for efficient modulation of the VCC PEF via the full size switcher 14.
What is needed is a power management system that meets the VCC BW requirements for a multi-carriers transmitter that uses envelope tracking or pseudo envelope following for intra band component carriers (CC) that are contiguous or non-contiguous within the band A and for inter band CC within the band A and within the band B. In particular, there is a need for a power management system that includes a switcher type power supply that extends the use of envelope tracking or pseudo envelope following for a modulation bandwidth greater than 20 MHz such as 2×20 MHz required for high data rate applications like those allowed with LTE-Advanced.